I’ve got a McCoy .19 red-head that is worn out and has poor compression.  MECOA sells Series 21 Black-Head pistons.  Will that work in my red-head?

  Many years ago I put a Series 40 piston and liner in my Red head 40, I changed piston and liner Series 21 and it fit the block, of the read head, if memory serves I also used the 21 head, you might give this a try on your 19...  Hope that this helps...

               Chris, the Mccoy uses a long plug, it could also use a long idle bar plug equally which is what I use in them. Thunderbolt r/c longs are very hot plugs and the Mccoy runs quite well on them. OS plugs are a bit different, even the long version OS is not as long as any other plug. I refer to them as a medium, they work well in their engines, but they don't always work as well in others. Only a few engines utilize short plugs. Mostly vintage 1/2A's and Fox .15's. They're really a rare breed.

What do you mean by “modify the head”—like counter-bore the top to take the shorter plug?

Yes, mill so short plug sits lower, properly oriented in combustion chamber.

My Enya .09-III head with a Swanson Associates Fireball Standard (long) plug and one washer. Cleared piston baffle, but the OS would probably fit better I gather.

Back to the engine itself, I think I recall that the .19 cylinder is attached with only two screws, having a four screw-hole head.  The Series 21 .19 has three cylinder screws.  I think it's the .29 and .35 that can be converted to the series 21 cylinder & piston, both having a six screw head.

Rod.

In any case, my Akromaster (with a good McCoy .19 on the front) has a nice 4-2 break.  Loops are much too large.  Like almost scrape the ground large. Is this due to 52’ lines or lack of flaps? I think the engine has plenty of power . .

Line length is not the problem, most likely engine weight. Is it nose heavy? Testor McCoy .19 Red Head weighs 6 oz. Fox .15-X weighs 3.6 oz.

I have the same problem with my Ringmaster Jr. It was designed for the lighter mufflerless .15's of the early 1950's, my OS Max .15FP-S weighs in the neighborhood of your McCoy.

Some have told me that .09-.10 Sport Schneurles are good on these smaller planes.

You can fly on 60' lines. Done that with my Ringmaster Jr., with more power similar to your .19, it still has good wind penetration without any problems on the longer lines.

Two (healthy) washers, for the long reach plug?

Oh, true, can shim plug. I took that photo some time back to show what the head portion of the combustion chamber looked like.

[THREAD HIJACK] Not using these Fireballs any more. I got a card of a dozen NOS Fireball plugs made some time ago may be 5 years ago off E-Bay, but alas, something's wrong with their catalyst coating. Works good first day out of the box. Wait a week, barely lights off and sputters. Never had that happen to me before with these plugs back in the late 1970's. They worked excellent especially for smaller A-size RC engines, from idle to full power. Looks like Swanson for this batch got a bad supplier of platinum coated nichrome wire. Yet the venerable Enya 30 plug that came with the engine fired right up no problems at all.

Seeing the heading is merely ' McCoy ', rumour has it the Merco 49 internals are near compatable with the Mc coy 49

Oh, wouldn't surprise me. Amazing some of the things folk have discovered. Example, I found that Evolution .46 rear needle valve assembly worked excellently on my McCoy .35 Red Heads, plugged needle valve side of the spray bar with a 2-56 screw, run fuel line to Evo RNVA, which bolt spacing fits backplate screw distance perfectly. Has a finer thread for easier tweaking of the mixture plus O-ring seal. [END HIJACK]

......rumour has it the Merco 49 internals are near compatable with the Mc coy 49 ,

I have a Merco muffler fitted to a McCoy Red Head .35.  Looks like it was made to fit.